I think it's only realistic not to expect that these films will feel like LoTR, at least as far as the first film is concerned. The tone of the films might change when we get further into nr. 2 and to nr. 3. It's only reasonable IMO to expect quite a bit of comedy mixed with action in the first film, especially as a way of identifying with the characters.

Both The Hobbit and LoTR have the same concept art designers, so I expect many of the places to look similar visually, but since The Hobbit is set in a more innocent time, it's natural that they try to differentiate it from the look and feel of LoTR in several respects. The choice about brighter colours, if my memory serves me right, is a choice that was made early on when Del Toro still was the director and has been kept as a way of differentiating The Hobbit from LoTR.

Seen in isolation, I understand that parts of the trailer might give a cause for concern, but I think it's wise not to worry too much based on the trailer, or any rumours. In the trailer we see so many things out of context and just for a split second.

When they're talking about having LoTR mesh with The Hobbit, it seems to me that they're talking about slightly expanding the context of the story in the Hobbit films so we see that it's clearly set in Middle Earth and is part of it's history, not about having exactly the same tone and feel as the LoTR films. But the use of music, the landscapes, the cultural diversity in the designs and the measures they use to develop the characters I expect to be mainly the same, so my theory is that those who liked Jackson's general concept of story-telling in the LoTR-films ought to like The Hobbit films as well, even if they haven't got the same scale and scope.

Not sure if I actually adressed any of your concerns, or in the way you wanted. I guess I've changed from slighly worrying to feeling more relaxed about the films in general.